1. Field of the Invention
The present invention relates to a computer program product, system, and method for preemptively allocating extents to a data set.
2. Description of the Related Art
In certain computing environments, multiple host systems may configure data sets in volumes configured in a storage system, such as interconnected storage devices, e.g., a Direct Access Storage Device (DASD), Redundant Array of Independent Disks (RAID), Just a Bunch of Disks (JBOD), etc. Data sets are comprised of extents, which may comprise any grouping of tracks and data storage units. The Z/OS® operating system from International Business Machines Corporation (“IBM”) includes Virtual Storage Access Method (VSAM) having a Direct Access Device Space Management (DADSM) routine which performs an extend operation to allocate a new extent to a data set if the current extent being written to in the data set has no more available space. (Z/OS is a registered trademark of IBM in the United States and other countries)
When the current extent being written has run out of available space, DADSM checks whether a data set can be allocated in a current volume in which the last data sets were allocated. If the DADSM determines that it cannot extend in the current volume either because the data set has reached a per volume extent limit for its data set type or the volume does not contain enough free space, then the DADSM needs to allocate a new extent in a different volume.
The operation to extend into a new volume can cause delays in writing to highly critical data sets while they have to wait for such operations to complete as ADDVOL, VOLUME SELECTION processing, and the complicated handshakes that must take place between components to complete the extend process into a different volume from the current volume in which extents were created.
There is a need in the art for improved techniques to allocate extents to a data set.